1. Field of the Invention
The present invention relates to diesel exhaust fluid (DEF) delivery systems, and, more particularly, to breather assemblies for such systems.
2. Description of the Related Art
As the Environmental Protection Agency (EPA) regulations covering combustion engine emissions are applied to ever more applications, the agricultural art and more broadly work machines are being required to comply with the EPA emissions limits already applied to on-highway vehicle applications. Many approaches have been proposed, but a cost-effective one is utilizing diesel exhaust fluid (DEF) injected into the exhaust stream of a diesel engine and providing a chemical reaction with the exhaust stream to enable a downstream SCR to produce appropriate reductions in nitrous oxide emissions.
One of the keys to this approach is the DEF delivery system. Current systems include a tank for the DEF, a pressure pump and a nozzle for injecting the DEF into the diesel exhaust system. Typical systems incorporate a control system for coordinating the injection of DEF with appropriate engine duty cycles so that the proper chemical reactions may take place. The DEF is typically a urea-aqueous solution that, while nonflammable, poses several application challenges.
The tanks for the DEF are rigid and as a result must include a breather assembly to permit ingress of air as the DEF is depleted from the tank. While this approach has been relatively straightforward for on-highway applications, the use in a work machine such as an agricultural combine presents unique problems. These problems are associated with the ambient air which has significant particulate contaminants of both a microscopic and macroscopic size. Existing systems may utilize hydrophobic membranes on the breather assembly to prevent outflow of the DEF vapors and condensate. However, such a system does not take into account the particulates that may be drawn into the breather assembly and clog the hydrophobic membrane. Such a restriction can cause the interior pressure of the DEF tank to be lowered to a point where proper delivery of the DEF to the exhaust flow is inhibited.
Likewise, breather assemblies that use a particulate filter permit DEF vapors and condensate to permeate the filter, thus causing crystal buildup and eventual clogging.
What is needed in the art, therefore, is a system for breather assemblies that operates efficiently and effectively in the work machine environment.